Improve Android Audio Recording quality?

At the moment, a big reason for poor audio quality recording on Android is the codec used by the MediaRecorder class (the AMR-NB codec). However, you can get access to uncompressed audio via the AudioRecord class, and record that into a file directly.

The Rehearsal Assistant app does this to save uncompressed audio into a WAV file - take a look at the RehearsalAudioRecord class source code.

The RehearsalAudioRecord class also provides a getMaxAmplitude method, which you can use to detect the maximum audio level since the last time you called the method (MediaRecorder also provides this method).

For recording and monitoring: You can use the sound recorder activity. Here's a snippet of code:

Intent recordIntent = new Intent(
                MediaStore.Audio.Media.RECORD_SOUND_ACTION);
            startActivityForResult(recordIntent, REQUEST_CODE_RECORD);

For a perfect working example of how to record audio which includes an input monitor, download the open source Ringdroid project: https://github.com/google/ringdroid

Look at the screenshots and you'll see the monitor.

For making the audio higher quality, you'd need a better mic. The built in mic can only capture so much (which is not that good). Again, look at the ringdroid project, glean some info from there. At that point you could implement some normalization and amplification routines to improve the sound.